I installed the WEMA sensors on 6 tanks on board (3 fuel
, 3 water) and didn't bother with putting a sensor in the holding tank as it's simple enough to look at the holding tank to see it's fill level.
The sensors seem to be bomb-proof, are simple to install provided you have clearance above the tank to drill the hole and install the sensor.
Accuracy is so-so, certainly good enough to distinguish tank volume in roughly 1/8 tank capacity increments. The issue seems (to me) that the collar that floats up and down on the vertical metal sensor rod sticks somewhat to the rod such that I'll be filling a tank and then the gauge will suddenly hop up abruptly - so I'm careful to avoid overfilling when attempting to fill a fuel tank completely, for example.
I do like the single
display that can be switched to indicate for all the different tanks - much better than having a dedicated gauge for each tank. This does mean you have to calibrate the gauge the gauge for each tank - half full in tank 2 might mean I have 18 gallons, and in tank 1 there might be 21 gallons. I made up a little drawing of the gauge for each tank, and if I really want to know what's in a particular tank then I switch to that tank, tap the display gauge, and refer to my drawing of that gauge for that tank.